1. Field of the Invention
The present invention relates to a technique for obtaining a waterproof ink image with decreased color-bleeding when a color image is formed on plain paper. In particular, it relates to an ink useful in image formation by means of an ink-jet recording process and apparatus using the ink.
2. Related Background Art
Ink-jet recording methods include recording by adhering ejected ink or inks to a recording medium such as paper. According to Japanese Patent Publication Nos. 61-59911, 61-59912, and 61-59914, a recording head having high density multi-orifices can be easily used in an ink-jet recording method in which liquid drops are discharged by forming bubbles in the ink by means of thermal energy from an electro-thermal transducer as the discharge energy supplying means. Moreover, an image having high resolution and high quality can be recorded at high speed.
However, conventional inks used for ink-jet recording generally include water as the major component and contain water-soluble solvents having a high boiling point, such as glycol, in order to prevent drying and clogging. Therefore, when recording on plain paper as the recording medium with such inks, the following problem occurs: The image cannot be satisfactorily fixed, and is not formed homogeneously, possibly due to non-homogeneous distribution of fillers and sizing agents on the recording medium surface. In particular, when forming color images, different color inks are continuously overlapped before each color ink is completely fixed on the paper. Thus, at the boundary section of different colors in the image, non-homogeneous color mixing (called "bleeding" below) is observed. Moreover, satisfactory water-proof printing has been increasingly demanded recently.
As a means for solving the above problems, the addition of a compound which improves permeability, such as a surfactant, to the inks is disclosed in Japanese Patent Laid-Open No. 55-65269. Further, an ink mainly containing volatile solvents is disclosed in Japanese Patent Laid-Open No. 55-66976. U.S. Pat. No. 5,106,416 discloses an ink containing a cation dyestuff, an ampholytic surfactant, and a nonionic amphiphilic compound. Moreover, U.S. Pat. No. 5,226,957 discloses an ink containing a water-insoluble dyestuff, a polymeric colloidal compound, and a surfactant. In addition, inks using betaine types of acrylic resins are disclosed in Japanese Patent Laid-Open Nos. 60-96673 and 4-139272.
When using the ink containing a compound, such as a surfactant, which improves the permeability of the ink into the recording paper, as described in the aforementioned Japanese Patent Laid-Open No. 55-65269, although fixing performance and bleeding resistance can be improved to some extent due to enhanced permeability of the ink into the recording paper, the ink permeates deep into the inside of the paper together with the coloring material. Therefore, there are some problems, such as decreased image density. Also decreased resolution and bleeding are observed at the same time, due to the horizontal spreading of the ink.
In the aforementioned Japanese Patent Laid-Open No. 55-66976, the nozzle in the recording head easily clogs due to the evaporation of the solvent, in addition to the above problems.
Although U.S. Pat. No. 5,106,416 intends to provide an ink containing a cation dyestuff, an ampholytic surfactant, and a nonionic amphiphilic compound, in which the diffusion of the coloring material is suppressed by the addition of the ampholytic surfactant in an amount that is at least equal to the critical micelle concentration or more, images obtained from this ink are not entirely satisfactory due to the enhanced permeability of the ink itself caused by the surfactant, similar to the aforementioned Japanese Patent Laid-Open No. 55-65269. In the ink containing a water-insoluble dyestuff, a polymeric colloidal compound, and a surfactant, disclosed in U.S. Pat. No. 5,226,957, the same disadvantages as well as the problems mentioned in U.S. Pat. No. 5,106,416 exist: Clogging in the head and nozzle occurs due to the precipitation of the water-insoluble dyestuff or coagulation of the colloidal compound.
Moreover, although the betaine types of acrylic resins are used to prevent bleeding of the oil-soluble ink in Japanese Patent Laid-Open No. 60-96673, or to improve the stability of the pigment ink in Japanese Patent Laid-Open No. 4-139272, high quality images cannot be achieved on plain paper.